Method of separating 2,6-naphthalic acid from 6-formyl-2-naphthoic acid

ABSTRACT

Mixtures of 6-formyl-2-naphthoic acid and 2,6-naphthalic acid formed from the oxidation of 2,6-dimethylnaphthalene are readily separable by the steam distillation of their esters. This method has a further advantage in that it removes trace amounts of color bodies from the aldehyde ester.

United States Patent McNelis et a1.

[451 Mar. 21, 1972 METHOD OF SEPARATING 2,6- NAPHTHALIC ACID FROM6-FORMYL- Z-NAPHTHOIC ACID Edward J. McNelis, New Rochelle, N.Y.; WesleyR. Cherry, Prospect Park, Pa.

Assignee: Sun Oil Company, Philadelphia, Pa.

Filed: Apr. 23, 1969 Appl. No.: 818,815

Inventors:

US. Cl. ..203/96, 260/469, 260/524 R, 260/524 N, 260/525 Int. Cl. ..B0ld3/38, C07c 67/06, C070 69/76 Field of Search ..260/475 B, 475 FR, 469,525, 260/524; 203/95, 96

References Cited UNITED STATES PATENTS McNerney Olivier et a1. Raecke eta1. Ackelsberg Levine ..260/524 Roberts et al. ..260/475 B LaboratoryTechnique in Organic Chemistry Avery Morton 1938 p. 143 QD261M74C5Laboratory Technique in Organic Chemistry Kenneth Wiberg 1960, pp. 71-74 Practical Organic Chemistry Arthur 1. Vogel Third Edition 1956, pp.12- 13, 15 QD251V6C3 Primary Examiner-Lorraine A. Weinberger AssistantExaminer-Jacqueline L. Davison Attorney-George L. Church, Donald R.Johnson, Wilmer E. McCorquodale, Jr. and Stanford M. Back ABSTRACTMixtures of 6-formyl-2-naphthoic acid and 2,6-naphthalic acid formedfrom the oxidation of 2,6-dimethylnaphthalene are readily separable bythe steam distillation of their esters. This method has a'furtheradvantage in that it removes trace amounts of color bodiesfrom thealdehyde ester.

4 Claims, No Drawings METHOD OF SEPARATING 2,6-NAPIITHALIC ACID FROM6-FORMYL'2-NAPI-ITIIOIC ACID BACKGROUND OF THE INVENTION This inventionrelates to a process for the separation of 6 formyl-Z-naphthoic acidfrom 2,6-naphthalic acid. More particularly, this invention relates tothe separation of the lower alkyl esters of 6-formyl-2-naphthoic acidand 2,6-naphthalic acid by steam distillation.

Mixtures of 6-formyl-2-naphthoic acid and 2,6-naphthalic acid arefrequently formed during the oxidation of 2,6- dimethylnaphthalene.Although the desired end product of this oxidation is 2,6-naphthalicacid, substantial amounts of the intermediate 6-formyl-2-naphthoic acidare often formed. Since it is necessary to separate out the 6-formylcompound in order to both purify the 2,6-naphthalic acid and to recyclethe 6-formyl intermediate for further oxidation, a clean and simplemethod for separating these two compounds has been sought.Unfortunately, however, because of the solubility of the fi-formylcompound and its other chemical characteristics, conventional techniquessuch as fractional distillation have proved difficult andunsatisfactory. Moreover, although selective crystallization of thediacid ester in alcohol has likewise been employed, this method at bestmerely provides recovery of just the 2,6-naphthalic acid, thus making itnecessary to utilize other techniques for recovering the 6-formyl-2-naphthoic acid.

SUMMARY OF THE INVENTION In accordance with the present invention, ithas now been found that 6-formyl-2-naphthoic acid (hereinafter aldacid)may be cleanly separated from 2,6-naphthlic acid (hereinafter diacid")by the steam distillation of their corresponding lower alkyl esterswhereby pure crystals of the aldacid compound may be recovered from thecondensate, leaving behind the diacid ester in substantially pure form.This method thus has not only the advantage of providing both of thecompounds in separate and pure form, but it also has the added advantageof providing the aldacid ester in a form which is free from traceamounts of colorbodies, which purity has not heretofore been possible bythe prior art methods.

DESCRIPTION OF THE INVENTION The mixture of the aldacid and diacid mayresult from a variety of processes. One such mixture to,which thepresent method is particularly applicable is that resulting from theoxidation of 2,6-dimethylnaphthalene with N either with or without aselenium dioxide catalyst, whereby a mixture of the aldacid and diacidare produced, often in equal amounts. It should be understood, however,that neither the source of the mixture nor the ratio of aldacid todiacid is critical to the success of the present method.

It is necessary that the diacid and aldacid be convened to theircorresponding lower alkyl esters prior to the steam distillation. Thisis conveniently achieved by treating the aforesaid mixture with asuitable esterifying agent, preferably an alkanol having from one tofive carbon atoms, and most preferably methanol. The reaction mayreadily be carried out in a steel or glass-lined bomb at an elevatedtemperature of from about to C.

Following removal of the excess alcohol and drying of the mixture, wateris then added to the diacid and aldacid esters and the mixture heateduntil steam is generated in situ, thereby accomplishing the steamdistillation. Alternatively, steam may be introduced into the mixturefrom an outside source. The amount of water or steam employed is notcritical; however, it is desirable that an excess of water or steam bemaintained throughout the distillation. The rate of recovery of thealdacid ester may be increased, if necessary, by the use of superheatedsteam.

Recovery of the diacid ester may conveniently be achieved by carryingout the steam distillation to extinction; the residue will then besubstantiallg pure diacid ester. Similarly, collectmg and drying the conensate will yield the aldacid ester in substantially pure form.

The invention will now be further illustrated by the following example.

EXAMPLE I A mixture comprising 1.22 g. of dimethyl 2,6-naphthalate and0.214 g. of methyl 6-formyl-2-naphthoate was mixed with 200 ml. ofwater. The mixture was seam distilled by the in situ method. Water wasreplenished as needed.

After 500 ml. of condensate the distillation was stopped, and 62 mg. ofwhite crystals were collected from the distillate and dried. Their IRmatched that of authentic aldacid methyl ester. They melted at 125-7 C.without crystallization (reported 129-30 C.

When the foregoing separation was carried out with superheated steam,the same results were observed, although at an increased distillationrate.

What is claimed is:

l. A method for the separation of a lower alkyl ester of 6-formyl-2-naphthoic acid from a lower alkyl ester of 2,6- naphthalic acidwhich comprises steam distilling a mixture of said esters and recoveringsaid ester of 6-formyl-2-naphthoic acid from the resulting condensate.

2. The process according to claim 1 wherein the steam is formed in situ.

3. The process according to claim I wherein the steam is introduced froman outside source.

4. The process according to claim 3 wherein the steam is superheatedsteam.

2. The process according to claim 1 wherein the steam is formed in situ.3. The process according to claim 1 wherein the steam is introduced froman outside source.
 4. The process according to claim 3 wherein the steamis superheated steam.